1. Field of the Invention
The present invention relates to a chemical vapor deposition (CVD) method and more particularly, to a method of cleaning a processing chamber after a refractory metal film is deposited on a substrate.
2. Description of the Related Art
As semiconductor devices have been developed to become more highly integrated, the design rule of such devices have decreased. Accordingly, parameters such as the channel length of transistors, the distance between active areas, the wiring width, the distance between wirings, and the size of contacts have been scaled-down. Based on the reduced size of the contacts, a certain type of metal silicide layer has been used to form low resistance contacts in semiconductor devices.
A metal silicide layer is an ohmic layer that can provide a low resistance interface between a silicon substrate and a metal layer formed on the silicon substrate. Also, a metal silicide layer may be formed between a metal layer and an underlying semiconductor region to reduce the possibility of materials in the metal layer and semiconductor region from diffusing into each other. A metal silicide layer can also reduce the possibility of such diffusion of materials between two different metal layers in a multilevel metal systems.
The silicide may be comprised of a material such as titanium silicide (TiSi2), or one of the group-VIII silicides such as PtSi2, PdSi2, CoSi2, NiSi2, etc. In a semiconductor device having a design rule of 0.25 xcexcm or less, titanium silicide is widely used for the metal silicide layers.
Conventionally, a heat treatment, e.g., rapid thermal process (RTP), is carried out after a sputtering process deposits a refractory metal film on an exposed silicon region of a substrate. The heat treatment forms a metal silicide layer between the refractory metal film and the silicon region. However, as the size of a contact hole decreases, and the aspect ratio of the contact hole increases, the sputtering process results in poor coverage of the refractory metal film at the stepped portion of the substrate. Thus, forming a sufficient metal silicide layer on the bottom of the contact hole is difficult.
In order to overcome the difficulty of step coverage due to the sputtering method, a method in which a refractory metal film is deposited using a chemical vapor deposition (CVD) or a plasma-enhanced CVD (PECVD) process has been suggested. During such a process, a metal silicide layer is formed while the refractory metal film is simultaneously deposited. Accordingly, even as the aspect ratio of the contact becomes higher, the refractory metal reacts with the silicon in the active region of the substrate to form a silicide without requiring a subsequent annealing process. This results in a simplified process for providing good step coverage.
However, during the PECVD process, the refractory metal film may also be deposited on surfaces inside the chamber in which the substrate is processed. For example, the refractory metal film may be deposited on the surface of various components in the chamber, including the shower head that supplies processing gases into the chamber, the heater that heats the substrate, etc. Accordingly, an in-situ dry cleaning process should be performed on the chamber after depositing the refractory metal film on the substrate in order to remove the refractory metal film remaining on surfaces inside the chamber.
A titanium silicide layer may be simultaneously formed while a titanium (Ti) film is deposited on the substrate according to a PECVD method using TICl4 gas. In such cases, after the PECVD process is performed, the chamber is in-situ cleaned by a dry cleaning process using Cl2 gas to thereby remove titanium films deposited on the interior surfaces of the chamber. Methods are disclosed in PCT Publication No. WO 1999-028955, Korean Patent Laid-Open Publication No. 2001-0007317, Korean Patent Laid-Open Publication No. 1998-087036, etc., in which the chamber is in-situ dry-cleaned to remove titanium films deposited on the inside of the chamber, after depositing the PECVD-Ti film.
However, such an in-situ cleaning process using Cl2 gas has the following disadvantages. The titanium film on the shower head surface may not be completely removed by the chamber cleaning because the titanium film contains a large quantity of chlorine (Cl) dissociated from TiCl4 gas. Further, chlorine atoms dissociated from Cl2 gas react with titanium atoms during the in-situ cleaning process, thereby generating reaction by-products such as TiClx (x=1xcx9c4) or Cl type impurities in high quantities. These reaction by-products remain in the chamber after the in-situ chamber cleaning is completed.
If the titanium film is not removed from the interior surfaces and reaction by-products remain after the chamber cleaning, the effectiveness of the PECVD-Ti process suffers when it is subsequently carried out on other wafers (or substrates). As a result, sheet resistance uniformity of the wafers and sheet resistance reproducibility of the titanium film become poor.
PCT Publication No. WO 1999-054522 discloses a method where NH3/H2/Ar plasma is formed in the chamber to remove cleaning gases and impurities left in the chamber after the PECVD chamber is in-situ cleaned with gases such as NH3, ClF3, Cl2, etc. However, since this method is used for periodically conditioning the PECVD chamber, the chamber cleaning is not performed after each and every wafer is processed. Thus, as the number of wafers being processed increases, unnecessary titanium films and reaction by-products continuously accumulate on the interior surfaces of the chamber, thereby deteriorating the PECVD-Ti film characteristics.
In an exemplary embodiment, the present invention provides a method of cleaning a processing chamber used for depositing a refractory metal film on a substrate by both plasma-treating the chamber with a gas including either nitrogen and/or hydrogen and in-situ cleaning the chamber.
In an exemplary embodiment, the chamber is plasma-treated with a gas including at least nitrogen to nitride any refractory metal film remaining in the interior of the chamber. The chamber is in-situ cleaned with a cleaning gas to remove the nitrided metal film from the chamber interior.
In exemplary embodiments, the method of the present invention may be used to clean a chamber that deposits a refractory metal film using a chemical vapor deposition (CVD) process. In an exemplary embodiment, a plasma-enhanced CVD (PECVD) process may be used to deposit a titanium (Ti) film on each substrate, for example, using titanium tetrachloride (TiCl4) gas. The cleaning gas may include a Cl2 gas to remove the nitrided Ti film from the chamber interior after a processed substrate is removed.
In an exemplary embodiment, the nitriding gas may also include hydrogen in order to dilute reaction by-products generated in the chamber when the refractory metal film is deposited on each substrate. According to another exemplary embodiment, after the refractory metal film is nitrided and the chamber is in-situ cleaned, the chamber may be plasma-treated with a third gas including either nitrogen and/or hydrogen. The third gas may include hydrogen for removing any reaction by-products remaining in the chamber as a result of the process of depositing the refractory metal film on the substrate, or removing reaction by-products generated as a result of the in-situ cleaning of the chamber. Also, the third gas may include nitrogen for further nitriding any refractory metal film remaining in the substrate after the in-situ cleaning.
In an exemplary embodiment, both the nitriding gas and the third gas may comprise gases including both nitrogen and hydrogen. For example, N2/H2 gas or NH3 gas may be used for both the nitriding gas and the third gas.
In another exemplary embodiment, the chamber may be used to deposit a refractory metal film on multiple substrates, successively. The steps of plasma-treating the chamber with the nitriding gas, in-situ cleaning the chamber, and plasma-treating the chamber may be repeated after each substrate is processed in the chamber
In another exemplary embodiment of the present invention, a chamber used for depositing a refractory metal film on a substrate may be in-situ cleaned with a cleaning gas, and then plasma-treated with a gas including at least hydrogen to remove reaction by-products generated during the processing of wafer and/or the in-situ cleaning. The chamber may be used for depositing the refractory metal film successively on a plurality of substrates, and the in-situ cleaning and plasma-treating steps may be performed after each substrate is processed. In another exemplary embodiment, the cleaning gas may include Cl2 gas, and the chamber may be plasma-treated with a gas including at least hydrogen and nitrogen in order to both remove reaction by-products from the chamber and to nitride any refractory metal film in the chamber.
By nitriding the refractory metal film remaining on interior surfaces of the chamber after processing and removing the wafer stable bonds between the nitrogen atoms and the refractory metal molecules (e.g., Ti atoms) suppress chorine (Cl) atoms dissociating from Cl2 gas from reacting with molecules in the refractory metal film. Thus, the generation of reaction by-product (e.g., TiClx or Cl-type compounds) is reduced when the chamber is in-situ cleaned with Cl2 gas. Furthermore, when the chamber is plasma-treated with a gas containing hydrogen, hydrogen ions in the plasma replace, and thereby reduce the amount of, chlorine Cl atoms in the surface of the refractory metal film. Accordingly, sheet resistance uniformity of the refractory metal film deposited on each processed substrate is improved, as well as sheet resistance reproducibility when multiple substrates are processed.